1. Field of the Invention
This invention relates to intraocular lenses of hydrogel material adapted for implantation in a human eye.
2. Discussion of the Prior Art
The concept of the use of intraocular lenses for the correction of aphakia has a long history. Much of the pioneering work was performed by Harold Ridley in London and by Binkhorst in the Netherlands. A comprehensive history of the development and results of the intraocular implant lens is presented by a thesis by Marcel Eugene Nordlohne and reproduced in Documenta Ophthalmologica, Vol. 38, Issue 1, Dec. 16, 1974.
A summary of the history of various artificial lens implants is also found in an article written by D. P. Choyce, published in the Annals of Ophthalmology, October, 1973, pages 1113-1120. In most cases lenses were made from organic high polymers such as, for example, poly(methyl methacrylate). It has also been proposed to implant glass lenses and to utilize lenses made of pure silicate glass. Specific glass compositions have been proposed in the disclosure of U.S. Pat. No. 3,996,627, for example. Although glasses have certain advantages as ocular implants, they are, in most cases, of a density rendering finished lenses relatively high in weight and less than optimum in this respect as implants. An early report by Schiferli in 1795 described an attempt by Casaamata to introduce a glass lens into the eye after a cataract operation. The lens immediately slipped back toward the fundus of the eye.
Many patents are addressed to the problem of mounting the intraocular lens within the eye so that it can perform its intended function with a minimum of trauma to the eye; see for example U.S. Pat. Nos. 2,834,023; 3,711,870; 3,673,616; 3,866,249; 3,906,511; and 3,913,148.
Intracameral lenses, i.e., prosthesis for the removed natural lens, fabricated of poly(methyl methacrylate) or of many glass-like materials generally are characterized by a refractive index value which is substantially greater than the refractive index value of 1.396 of the natural crystalline lens of a human eye. For example, intraocular lenses of the poly(methyl methacrylate) type possess a refractive index in the area of 1.53. Thus, the geometry and shape of an intraocular implant lens of the poly(methyl methacrylate) type differ from that of a natural lens to enable the artificial lens immersed in the refracting medium (the aqueous humor and vitreous humor) to substantially duplicate the refractive index characteristic of the natural lens. For example, the artificial lens is shaped with substantially smaller curvatures of both optical surfaces than is the case with the natural lens. However, such changes in shape of the artificial lens precludes implantation in the exact position of the space occupied by the natural lens. Further disparity is noted in the specific weights of conventional material, e.g., about 1.25, used in the fabrication of intraocular lenses compared with the specific weight of the natural lens (about 1.1). Thus an IOL implant of conventional material immersed in the refracting medium of the eye appears several times heavier than the natural lens. This disadvantage has been diminished by the recent practice of designing thin intracameral lenses which, however, further increases the diversity of shape between the artificial lens and the natural lens.
Many adaptations have been proposed, and several actually used, to hold a miniaturized but relatively heavy intraocular lens system (body and mounting or securing means) in the desired optical zone. Pat. No. 4,073,015 discloses the mounting and securing of an intraocular lens so as to hold it in place permanently without lasting irritation to the patient. The patentees state that the lens is made of acrylic, hydrogel, or other biologically tolerable lens material and is formed with laterally extending planar flanges or haptical portions. A woven or knitted fibrous material, such as Dacron, is attached to the outer perimeter of the haptical portions and provide sites into which tissue of the iris can grow so as to form a permanent anchor for the lens; see column 1, line 66 to column 2, line 7 of U.S. Pat. No. 4,073,015. The intraocular lens structure and lens mounting system (lens body, integral haptical portion, loops, etc.) is inserted into the location previously occupied by the crystalline lens by expanding the pupillary opening of the iris to admit the said system; column 3, lines 56-66 of U.S. Pat. No. 4,073,015. It is apparent from the specification and drawings that the lens body of the patentees' intraocular lens system is significantly smaller than the natural lens of the patient's eye.